updated 07:12 pm EST, Fri December 28, 2012

Fourth of 13 total gifts for UK, Canada, Europe users

Apple's 12 Days of Christmas app, available only in Canada, Mexico, the UK, Australia and New Zealand and parts of Europe, added to its list of gifts with a free HD episode of the critically-acclaimed BBC Drama Sherlock, starring Benedict Cumberbatch and Martin Freeman. The episode in question, "A Study in Pink," is loosely based on the classic novel "A Study in Scarlet" by Sir Arthur Conan Doyle. It originally aired as one of three episodes in the show's first series.

The show, made by many of the same people responsible for Doctor Who, has found a similar worldwide audience. The first and second series were sold to over 180 countries and territories, and filming for a third series is underway. Both Freeman and Cumberbatch have also found movie stardom, with the latter appearing in the forthcoming Star Trek Into Darkness film, while the former is the title character in Peter Jackson's new epic, The Hobbit.

There are occasional regional differences in the gifts given out during the promotion. In Mexico, for example, the Sherlock episode was replaced with a free educational app called Geo Master 2, according to a MacNN reader report. Another report from New Zealand says that tomorrow's gift is a free cookbook, though North American users will have to wait until midnight PST to find out if that's the case for their region.

The Sherlock episode is normally available for download at a cost of $5 ($7 for HD), while the whole series (consisting of three 90-minute episodes) is available for $10 (or $13 for HD). Previous gifts in the 12 Days of Christmas app have included soccer game Score!, a free Maroon 5 EP, and a music video of Rod Stewart singing "Let it Snow."